Microelectromechanical (MEMS) devices have found many applications in basic signal transductions. For example, MEMS-based spatial light modulators are transducers that modulate incident light in a spatial pattern in response to optical or electrical inputs. The incident light may be modulated in phase, intensity, polarization, or direction. This modulation may be accomplished through the use of a variety of materials exhibiting magneto-optic, electro-optic, or elastic properties. Such spatial light modulators have many applications, including optical information processing, display systems, and electrostatic printing.
A micromirror-based spatial light modulator is a spatial light modulator consists of an array of micromirrors and an array of electrodes and circuits. A typical micromirror has a deformable reflective mirror plate attached to a deformable hinge that is held on a substrate such that the mirror plate can rotate to different positions. According to the different rotation positions of the mirror plate, operation states, such as ON and OFF states in a binary operation mode are defined. In the ON state, incident light is reflected so as to produce a “bright” pixel on a display target, and in the OFF state, incident light is reflected to produce a “dark” pixel on the display target. In an application of displaying an image represented by image pixels having “bright” and “dark” values, the micromirrors are associated with the image pixels, and the micromirrors are individually set to the ON or OFF states according to the “bright” or “dark” values of the image pixels associated with micromirrors. The collective effect of the reflection from the micromirrors at the ON and OFF states for a given incident light is reproduction of the image on the display target.
The deflections of the mirror plates are accomplished through the electrodes and circuits connected to the electrodes. Specifically, each mirror plate of a micromirror is electrostatically coupled to one or more electrodes such that an electrostatic field can be established between the mirror plate and the electrode(s) for deflecting the mirror plate. The strength of the electrostatic field is determined by the voltage of the electrode, and voltage of the electrode is controlled by the output voltage of the circuit, which can be a memory cell, such as a DRAM. With this configuration, the micromirrors can thus be individually addressed and the mirror plates of the micromirrors can be individually deflected.
Currently, a variety of micromirror-based spatial light modulators have been developed. For example, a spatial light modulator may have the micromirrors and electrodes formed on separate substrates. In particular, the micromirrors are formed on a light transmissive substrate, while the electrodes and circuitry are formed on a standard semiconductor substrate. An advantage of this configuration is that the micromirrors can be fabricated on the light transmissive substrate using a separate fabrication process from the process for fabricating the electrodes and circuitry on the semiconductor substrate. Therefore, most suitable fabrication processes can be respectively designed for the micromirrors and the electrodes and circuitry. After separate fabrications of the micromirrors and electrodes and circuitry, the substrates are assembled together to form a micromirror array device.
In industrial manufacturing, the micromirrors are fabricated in dies on a light transmissive wafer with each die comprising an array of micromirrors. Likewise, the electrodes and circuitry are also formed in dies on a semiconductor wafer with each die having an array of electrodes and circuitry. After the fabrications of the micromirrors and electrodes, the micromirror dies and the electrode dies can be assembled on the wafer level. The assembled micromirror dies and electrode dies on the assembled wafers are then separated into individual die assemblies. Such a wafer-level assembling method, however, raises a die matching problem in a situation that not all dies on a wafer are passing dies.
Often times, not all the dies on a wafer (e.g. the micromirror wafer and the electrode wafer) are passing dies, such as the dies satisfying pre-determined product quality and performance requirements. Moreover, locations of the passing (or non-passing) dies on wafers vary from wafer to wafer. As a result, a passing die on one wafer may be assembled with a non-passing die on another wafer, resulting in reduction of the production yield.
Therefore, what is desired is a die matching mechanism for matching the dies on different wafers while maximize the production yield.